This invention relates to improved reflectivity and resolution X-ray dispersive and reflective structures for carbon, beryllium and boron analysis. These synthetic structures are free from the constraints of crystalline symmetries and from the restrictive prior art vapor deposition techniques and materials. The improved structures provide improved characteristics for the specific analysis designed for.
Commercial X-ray dispersive structures are formed from crystalline structures such as LiF, metal acid phthalates (map), pyrolytic graphite and Langmuir-Blodgett (LB) films. These materials have very restrictive lattice spacing constraints. In addition, the LB and map devices have severe environmental limitations and must be operated near room temperature in a dry environment. LB devices are not appropriate for very high vacuum applications since under certain conditions they can evolve contaminants. They are also inappropriate for high incident beam energy applications since they can decompose. They have poor mechanical integrity, such as scratch resistance, mechanical breaking strength and resistance to abrasion. Further, all of the prior structures have lower reflectivities than desired.
Numerous attempts to construct both natural and new crystalline analogue materials have been made with the aim of extending the X-ray properties heretofore limited by the availability of natural crystalline materials. One such attempt is compositional modulation by molecular beam epitaxy (MBE) deposition on single crystal substrates. For example, in Dingle et al., U.S. Pat. No. 4,261,771, the fabrication of monolayer semiconductors by one MBE technique is described. These modulated prior art structures are typically called "superlattices." Superlattices are developed on the concept of layers of materials forming homo or hetero epitaxially grown planes or film layers resulting in a one-dimensional periodic potential. Typically, the largest period in these superlattices is on the order of a few hundred Angstroms; however, monatomic layered structures have also been constructed.
The superlattices can be characterized by the format of a number of layer pairs formed by a layer of A (such as GaAs) followed by a layer of B (such as AlAs), etc.; formed on a single crystal synthetic material with good crystalline quality and long range order. The thickness of each layer pair (A and B) is defined as the "d" spacing. These structures are not appropriate for most reflective or dispersive structures due to the small electron density contrast between the layers. These structures being essentially single crystals with extra super lattice periodicities also suffer from restrictive d spacing, associated with the constraint that the entire structure be a single crystal.
In addition to the MBE type of superlattices construction techniques, other researchers have developed layered synthetic microstructures (lsm) utilizing other forms of vapor deposition, including diode and magnetron sputtering, reactive gas injection and standard multisource evaporation. The layer dimensions are controlled by shutters or moving the substrates relative to the material sources or with combinations of shutters and relative motion. In the case of multisource evaporation, the required thickness control is achieved by monitoring the X-ray reflectivity of the film in situ as the deposition is being made. The materials reported have been formed from crystalline layers, noncrystalline layers and mixtures thereof; however, generally the efforts so far reported are directed at the synthesis of superlattice-type structures by precisely reproducing the deposition conditions on a periodic reoccurring basis. Some of the structures have graded d spacing through the structure.
These materials can be thought of as synthetic crystals or crystal analogues in which it is defined as crucial that the long range periodicity or repetition of a particular combination of layers be maintained. These structures are both structurally and chemically homogeneous in the x-y plane, and are periodic in the third (z) direction. These construction approaches particularly sputtering, can utilize a greater variety of materials than evaporation.